Employing prospective data, this project seeks relationships between adolescent personality and family size. The effects of biological-maturational, cognitive, and socio-demographic attributes are also to be evaluated. The data are drawn from the archives of the Institute of Human Development at the University of California, Berkeley, and provide comprehensive and longitudinally-gathered assessments of two normal samples of men and women studied throughout their early development into later adulthood. We will determine the overall power of adolescent personality for the prediction of family size, highlight which specific personality dimensions are most critical in this prediction, and examine possible differences in genotypic continuity of personality within individuals who rear smaller versus larger families. Family size will also be related to the psychological health of the study participants at two points during adolescence and at adulthood. Personality attributes of the spouses and children of the participants, as they may relate to family size, will also be considered. Our results, in their raw form, will of course, be cohort-specific, but the theoretical understandings we expect to achieve regarding adolescent personality and family size should generate testable hypotheses relevant to parenting behavior in current and future cohorts.